Substrate with an electrode and method of producing the same

ABSTRACT

The present invention provides a method of forming a transparent conductive film at a low temperature that is suitable for use with a synthetic resin substrate. According to the production method of a substrate with an electrode of the present invention, an oxide conductive film composed of an amorphous material or mainly composed of an amorphous material is formed on a substrate at a temperature equal to or less than the crystallization temperature of the film, and subsequently, the formed oxide conductive film is crystallized by heating. The oxide conductive film is processed into the shape of an electrode either before or after crystallization, according to necessity.

TECHNICAL FIELD

[0001] The present invention relates to a substrate having an electrodeon a surface thereof and more particularly, to an improvement in amethod for forming an electrode on a substrate.

BACKGROUND ART

[0002] In display devices such as liquid crystal display (LCD),electrochromic display (ECD), plasma display (PDP), andelectroluminescent display (ELD) devices and inmetal-insulator-semiconductor (MIS) solar cells, transparent electrodesare generally formed on the surface of a substrate made of glass or thelike. A transparent film with low resistance can be obtained using ametal such as silver, but in order to ensure sufficient lighttransmissivity, it is necessary to form an extremely thin film having athickness of approximately 10 nm. Difficulties, however, arise in thehandling of such a thin film, as such a film can be easily damaged insubsequent steps such as in a step of patterning the electrodes. Forthese reasons, an oxide conductive material such as zinc oxide, indiumoxide, or tin doped indium oxide (ITO), which although has a highresistivity in comparison to metal, has a high hardness and is notparticularly susceptible to deterioration in function caused by oxidedegradation, is used for the transparent electrodes formed on asubstrate. In particular, films made of ITO are widely used because ofthe low resistivity thereof. In ITO, Sn⁴⁺, which substitutes for In³⁺ inoxide indium In₂O₃, generates a carrier electron. As is the case withindium oxide, the crystal structure is a cubic bixbyite structure. Forthe formation of an ITO film, sputtering, which enables the formation ofa low resistance film on a substrate with a large area at a relativelylow temperature, is generally employed. The characteristics of a filmformed by sputtering vary according to the substrate temperature duringformation. A film formed at a high temperature of approximately 200° C.or higher is a so-called polycrystalline film made up of an aggregate ofmicrocrystal. In such a film formed at a high temperature, microcrystalsin each of certain regions orient in substantially the same direction,thereby forming domains. A temperature of 250° C. has been determined tobe the substrate temperature at which a film having both the highestpossible transparency and the lowest possible resistance can beobtained. By contrast, a film formed at a low temperature is amorphousor has a structure mainly in an amorphous phase with crystal fine grainsbeing dispersed therein. While an amorphous film has excellentetchability for the processing of electrodes, fundamentalcharacteristics such as conductivity and transparency are inferior tothose of a polycrystalline film. Chemical resistance and corrosionresistance are also inferior. In a film that is a mixture of theamorphous phase and the crystal phase, linearity of film patterning ispoor because the etching speed for each phase differs greatly. In, forexample, cases in which crystal grains are dispersed in an amorphousmatrix, it is only the crystal phase that is not etched, remaining asresidue and becoming a cause of defects. In addition, because most ofthe film is the amorphous phase, the film is inferior in terms of avariety of properties such as conductivity, transmissivity, chemicalresistance, corrosion resistance, and durability.

[0003] For example, in Japanese Unexamined Patent Publication No.4-48516, it is proposed that, for the transparent electrodes, an ITOfilm or an indium oxide film, each being oriented in a specifieddirection and having excellent patternability for etching, be employed.In the same publication, an amorphous film is proposed as an electrodematerial having excellent patternability for etching. While an amorphousfilm has excellent etchability, it is inferior in terms of fundamentalcharacteristics such as conductivity and transparency. In JapaneseUnexamined Patent Publication No. 8-94230, a randomly-orientedpolycrystalline ITO film formed by sputtering at a substrate temperatureof 180-350° C. is proposed as a transparent conductive film havingexcellent etchability.

[0004] As in the above examples, polycrystalline films for electrodeshave conventionally been formed by sputtering with the substratetemperature fixed at a high temperature of 200° C. or higher. Thus, itwas necessary to employ a substrate made of a material capable ofwithstanding a high temperature of 200° C. or higher during formation ofa film, such as a substrate made of glass.

[0005] In recent years, many attempts have been made to use a substratemade of a synthetic resin rather than a substrate made of glass, as asynthetic resin substrate has the advantages of being light weight anddifficult to break. However, synthetic resin substrates can withstand atmost a temperature of 180° C. Therefore, it is not possible to form, ona surface of the substrate, a transparent conductive film made of anoxide such as ITO or zinc oxide at high temperatures of 200° C. orhigher. Namely, electrodes formed on a synthetic resin substrate had tobe either a film in which the amorphous phase and the crystal phase aremixed or a film in the amorphous phase. In Japanese Unexamined PatentPublication No. 9-61836, a method is proposed wherein, by mixing H₂O ina sputtering gas, an ITO thin film having excellent etchability and alow density of crystal grains dispersed in an amorphous matrix is formedon a synthetic resin substrate. This film, however, also is inferior toa polycrystalline film formed at a high temperature in terms ofconductivity and transparency.

[0006] In Japanese Unexamined Patent Publication No. 5-346575, a methodis proposed wherein resistance is improved by using vapor deposition toform an ITO film on a synthetic resin substrate at a temperature belowthe temperature at which the substrate undergoes a change in shape andcalcining the film in air to adjust the degree of oxidization. However,with this method also, fundamental characteristics such as resistivityand transmissivity are insufficient in the resulting film.

[0007] The temperature of heating is limited, not only in cases wheresubstrates made of synthetic resin are used, but also in cases where acolor filter layer and a light-emitting layer made of an organicmaterial are provided on a same substrate. For example, a transparentconductive film for use as the electrodes of a super twisted nematic(STN) mode color LCD is formed on a color filter made of organicmaterial. The substrate temperature during the forming of thistransparent conductive film is limited to approximately 200° C. or lessdue to the presence of the color filter material.

[0008] Thus, there has been a need for a method of forming, at a lowtemperature, a conductive film that has excellent resistivity,transmissivity, etchability, and the like.

[0009] In addition, because of the difference in the thermal expansioncoefficient of a substrate and a conductive thin film formed on thesurface of the substrate, the substrate is susceptible to bend. Whenbend arises in a substrate, precision in the processing of the formedconductive thin film into electrodes is reduced. The higher thetemperature during formation of the conductive thin film, the larger thebend becomes. In other words, when the film is formed at a lowtemperature, while bend in the substrate is minimal, a film withsufficient characteristics cannot be obtained. In amorphous silicon(a-Si) solar cells in which a transparent conductive film, an amorphoussilicon layer, and an aluminum electrode layer are stacked on asubstrate, in organic ELDs in which a pair of electrode layers and anorganic light-emitting layer sandwiched therebetween are stacked on asubstrate, and the like, precision in the processing of other layersstacked on the conductive thin films suffers. In any case, in order toobtain a high wiring density and a stable internal resistance, it isabsolutely necessary that such a bend be reduced. In particular, in a-Sisolar cells, which are set up outside, good reliability and durabilityare required, making bend a serious problem.

[0010] Synthetic resin substrates are more susceptible to bend than areglass substrates. For this reason, the formation of conductive thinfilms on synthetic resin substrates has conventionally been carried outin the relatively low range of from room temperature to 150° C. In orderto meet the demand for a reduction in the size, a reduction in theweight, and an improvement in light transmissivity of display panels, itis necessary that the thickness of the substrates be reduced. At thesame time, in order to reduce the internal resistance of a circuit, itis necessary that the thickness of conductive films for electrodes andthe like be increased. Thus, as reduction in the size and improvement inthe performance of devices progress, the more serious a problem bend insubstrates and fractures and the like that arise along with bend become.

[0011] In Japanese Unexamined Patent Publication No. 2000-222944, amethod of forming a low stress and low resistance ITO film is proposedwith the aim of preventing fractures in the thin film. In this method,under the condition that the substrate temperature be approximately 200°C., a polycrystalline film made up of an aggregate of polygonalcolumn-shaped crystal grains is formed by ion plating with arc dischargeplasma. Although this method is effective for preventing fractures inthe thin film, it is not effective for suppressing the bend in asubstrate that arises with heating at a high temperature. It is alsodifficult to use this method for forming a film at a low temperature ona substrate made of synthetic resin. Thus, there has been a need for amethod of forming, at a low temperature, a conductive thin film havingexcellent resistivity, transmissivity, etchability, and the like, thatdoes not also bring about a change in the shape of the substrate.

DISCLOSURE OF THE INVENTION

[0012] In order to overcome the foregoing problems, it is an object ofthe present invention to provide a method of forming, at a lowtemperature, a conductive film that is especially useful when utilizinga synthetic resin substrate and that is excellent in terms of a varietyof properties such as resistivity, transmissivity, chemical resistance,corrosion resistance, patternability, and adhesion. It is another objectof the present invention to provide a method of forming a conductivefilm wherein the forming of the film on a substrate renders a substratein which bend is small.

[0013] According to a method of producing a substrate with an electrodeof the present invention, an oxide conducive film composed of anamorphous material or mainly composed of an amorphous material is formedon a substrate at a temperature equal to or less than thecrystallization temperature of the film, and subsequently the formedoxide conductive film is crystallized by heating. The oxide conductivefilm is processed into the shape of an electrode either before or afterthe crystallization, according to necessity.

[0014] According to the present invention, crystals in the film aregrown in a step subsequent to film formation, making it possible to formthe film at a low temperature. The amount of stress that arises in theformed film is dependant on the degree of change in shape of thesubstrate during formation of the film, i.e., the substrate temperature.Formation of the film at an even lower temperature is effective forsuppressing bend in the substrate. Preferably, the film is formed at atemperature of 150° C. or less, because a substrate with an electrodehaving a small bend, excellent adhesion, and high reliability canthereby be obtained, owing to the fact that internal stress in thetransparent conductive film caused by the change in shape of thesubstrate with heating is small. In particular, when a synthetic resinsubstrate, which is susceptible to change in shape, is used, it ispossible to significantly reduce bend in the substrate by forming thefilm at normal temperature.

[0015] The crystallization of the oxide conductive film is carried outby heating the oxide conductive film. It is not always necessary tocarry out crystallization at a temperature equal to or higher than thecrystallization temperature. From the standpoint of the amount of timerequired for the treatment, the crystallization is preferably carriedout at a temperature equal to or less than the maximum temperature thesubstrate can withstand, such as the glass transition temperature of thesubstrate, specifically a temperature in the range of 150° C.-200° C.,though it is also possible to carry out the crystallization at atemperature less than this temperature range. It is, of course,preferable that the temperature be equal to or higher than the substratetemperature during the formation of the film. The step of crystallizingthe oxide conductive film may be carried out under an atmospherecontaining oxygen or an atmosphere not containing oxygen.

[0016] The oxide conductive film formed on the substrate is made of, forexample, indium oxide or indium oxide having a portion substituted bytin (ITO). In order to effectively crystallize the oxide conductive filmat a low temperature, the film is made to have a tin oxide content ofless than 5% by weight. When the added amount of tin is made small, thecrystallization temperature is reduced, thereby making it possible toeven more effectively carry out the crystallization treatment at a lowtemperature. In conventional production of a thin film by sputtering, alow tin oxide content results in an increased resistivity, but in thepresent invention, crystallization of the film is brought about by atreatment carried out after film formation, making it possible to obtainan ITO film having a low resistivity even when the tin oxide content islow.

[0017] The size of a single crystal grain after crystallization isdetermined by the crystal state of the film immediately after formationof the film on the substrate, in other words, by the size of the finecrystal grains dispersed in the amorphous matrix and the dispersiondensity. In order to form a polycrystalline film that has an averagegrain size of 20-300 nm and random orientation and that has excellenttransmissivity, conductivity, etchability, and the like, and lowinternal stress, it is desirable that the oxide conductive film have astructure wherein, at the stage immediately after the formation of thefilm on the substrate, crystal grains having an average grain size of200 nm or less are dispersed in an amorphous matrix. Modification in thesize of crystal grains dispersed in the amorphous matrix and thedispersion density is made possible by varying conditions such assubstrate temperature, gas pressure, and production speed duringformation of the film. These conditions are determined according toelectrode material.

[0018] The present invention is particularly useful for the productionof a substrate with an electrode that utilizes a synthetic resinsubstrate with which formation of a film at a low temperature isrequired.

[0019] It is preferable that an undercoat layer made of an organicmaterial be provided on a surface of a substrate to relieve stresscaused by the difference in the coefficient of thermal expansion betweenthe substrate and the electrode formed thereon.

[0020] Forming a transparent coating film containing a synthetic resinon the surface of the completed electrode is effective for suppressingbend in a substrate. As long as the volume resistance of thistransparent coating film is 10²-10¹² Ω·cm or less, damage to electrodefunction is substantially nonexistent. Because a substrate provided witha transparent coating film is not susceptible to bend even with a changein temperature, use of a substrate of the present invention forsubstrates of display panels such as LCD and organic ELD panels makes ahigh quality display in a wide temperature range possible. It should benoted that providing the transparent coating film so as to cover theelectrode prevents damage to the electrode in subsequent steps, therebymaking it possible to use conductive materials other than oxideconductive materials, such as metal, for the electrode material. Inparticular, when an extremely thin metal film is used for a transparentelectrode or a translucent electrode, the film formed on the surface ofthis metal film serves as a protection film for preventing damage to themetal film in subsequent steps.

[0021] For example, a resist is used for the transparent coating filmthat is formed on the surface of the electrode. A resist layercontaining a light-curing resin is formed on the completed conductivefilm, regions corresponding to an electrode pattern for processing theoxide conductive film are cured by exposure to thus form the transparentcoating film, and the oxide conductive film is etched using the curedtransparent coating film as a resist. The etching thus makes it possibleto form a transparent coating film that covers the electrode and has ashape that substantially conforms to that of the electrode,simultaneously with processing the conductive film into electrode. Inthis way, it is not necessary to add an additional step in order to forma transparent coating film. A step of removing the resist may also beomitted.

[0022] Use of a light-curing resin in which conductive powder isdispersed makes it possible to obtain a transparent conductive filmhaving a desired volume resistance.

[0023] When the thickness of the transparent coating film is 0.5-5 μm, agood display is possible even if a substrate having such a film formedthereon is utilized as the substrates for a liquid crystal panel.

[0024] A substrate with an electrode of the present invention comprisesa substrate and an electrode made of an oxide conductive film disposedon the substrate, the electrode being composed of a polycrystalline filmhaving an average grain size of 25 nm or larger, preferably 40 nm orlarger, where a crystal is the largest constitutional unit having aboundary identifiable by surface observation. In other words, thepolycrystalline film does not have so-called domains, aggregates ofcrystal having a substantially aligned orientation direction. In such afilm, because stress arising in the conductive film is small compared toconventional transparent conductive films having grains, the film is notparticularly susceptible to cracks and fractures caused by stress. Bendin the substrate is also small.

[0025] In particular, in comparison to an amorphous film, a conductivefilm with which a clear diffraction peak has been confirmed by X-rayanalysis, verifying an average crystal grain size of 20 nm or larger,has a low resistance, excellent transmissivity, excellent chemicalresistance, and excellent corrosion resistance. In addition, the filmdoes not have uneven distortion, and thus has excellent linearity inpatterning. The average grain size of the crystals is preferably 300 nmor less.

[0026] When the thickness of the electrodes is as thin as less than 15nm, the progress of the crystallization by heating is particularly slow.On the other hand, when crystallization is carried out at a hightemperature on a thick film having a thickness that exceeds 1,500 nm,breaks and fractures are more likely to arise. Furthermore, suchcrystallization deepens corrugations in the surface of the film.Therefore, in order to ensure sufficient conductivity while moreeffectively preventing fractures in the film and bend in the substrate,it is preferable that the thickness of the formed oxide conductive filmbe 15-1,500 nm, and more preferably, 50-500 nm. When the heightvariation of the surface of the electrode is 20 nm or less, a devicewith stable characteristics can be obtained. For the oxide conductivefilm, ITO can be used, preferably having a tin oxide content of lessthan 5% by weight.

[0027] Coating the surface of the electrode by disposing a transparentcoating film that contains a synthetic resin and has a volume resistancein the range of 10²-10¹² Ω·cm is effective in protecting the electrode.When the substrate is made of a synthetic resin, this coating of thesubstrate surface makes is possible to suppress change in the shape ofthe substrate caused by thermal expansion, as the electrode is thensandwiched between synthetic resin having similar coefficients ofthermal expansion.

[0028] In order to function as a protection film for an easily damagedmetal electrode, it is preferable that the thickness be 0.5 μm orgreater. When used in a display panel, the thickness is preferably 5 μmor less so that image quality is not affected. As for volume resistance,when film thickness is 5 μm, it is preferable that volume resistance be10¹² Ω·cm or less. In the case of using a metal film for a transparentelectrode, thickness of the metal film is preferably 20 nm or less, andmore preferably, 10 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a longitudinal section schematically showing theconstruction of a liquid crystal display panel that utilizes substrateswith electrodes of one example of the present invention.

[0030]FIG. 2 is a scanning electron microscope picture showing thesurface of an ITO thin film obtained in the same example.

[0031]FIG. 3 is a longitudinal section schematically showing theconstruction of a liquid crystal display panel that utilizes substrateswith electrodes of another example of the present invention.

[0032]FIG. 4 is a longitudinal section schematically showing theconstruction of a liquid crystal display panel that utilizes substrateswith electrodes of yet another example of the present invention.

[0033]FIG. 5 is a longitudinal section schematically showing theconstruction of a liquid crystal display panel that utilizes substrateswith electrodes of still another example of the present invention.

[0034]FIGS. 6a and 6 b are each a longitudinal section schematicallyshowing the state of a substrate in one step of a production method forthe same substrate with electrodes.

[0035]FIG. 7 is a longitudinal section schematically showing theconstruction of an organic EL display panel.

[0036]FIG. 8 is a scanning electron microscope picture showing thesurface of an ITO thin film formed in a comparative example.

REFERENCE NUMERALS

[0037]1 liquid crystal display panel

[0038]2 a array substrate

[0039]2 b counter substrate

[0040]3, 103 liquid crystal layer

[0041]4 spacer

[0042]5 a, 5 b, 105, 205 substrate

[0043]6 a, 6 b undercoat layer

[0044]7 a, 7 b electrode

[0045]8 a, 8 b, 108 a, 108 b alignment film

[0046]10 buffer layer

[0047]11 color filter layer

[0048]12 resin layer

[0049]13 insulating layer

[0050]100, 208 conductive coating film

[0051]101, 101 a, 101 b substrate with electrodes

[0052]102 metal film

[0053]102 a, 202 transparent electrode

[0054]102 b translucent electrode

[0055]109 polarizer

[0056]200 light-emitting region

[0057]204 light-emitting layer

[0058]205 electron transporting layer

[0059]206 hole injecting layer

BEST MODE FOR CARRYING OUT THE INVENTION

[0060] The preferred embodiments of the present invention are describedin detail below with reference to the figures. In the followingexamples, substrates for liquid crystal display panels are used asexamples of substrates with electrodes.

EXAMPLE 1

[0061] A liquid crystal display panel that utilizes substrates withelectrodes of the present example is shown in FIG. 1.

[0062] As shown in FIG. 1, a liquid crystal display panel 1 has a pairof opposing substrates, specifically an array substrate 2 a and acounter substrate 2 b, and a liquid crystal layer 3 sandwiched betweenthe substrates. The substrates 2 a and 2 b are held at a fixed distancefrom one another by spherical spacers 4.

[0063] The array substrate 2 a has a substrate 5 a, an undercoat layer 6a, serving as a gas barrier film, disposed on a surface of the substrate5 a opposed to the counter substrate 2 b, film electrodes 7 a made of atransparent conductive material, and an alignment film 8 a made ofpolyimide or the like. Similarly, the counter substrate 2 b has asubstrate 5 b, an undercoat layer 6 b, serving as a gas barrier film,electrodes 7 b, and an alignment film 8 b.

[0064] The substrates 5 a and 5 b both have a thickness of 0.4 mm andare made of an acrylic resin having a glass transition temperature of190° C. The undercoat layers 6 a and 6 b are both made of a siliconoxide film having a thickness of 20 nm that is formed by sputtering.Both the electrodes 7 a and the electrodes 7 b are made of an ITO filmcontaining 5% by weight of tin oxide and having a thickness of 150 nm.

[0065] On a surface of the substrate 5 a, under the conditions shown inTable 1, a film made of ITO containing 5% by weight of tin oxide wasformed to a thickness of 150 nm by sputtering. Specifically, withoutheating the substrate 5 a, the film was formed by sputtering on thesurface at a rate of 6 nm/min. and under an atmosphere containing argonand oxygen at a pressure of 3.0×10⁻³ Torr (≈0.4 Pa).

[0066] Through observation with a scanning electron microscope (SEM), itwas confirmed that the formed ITO film had a structure such thatmicrocrystalline grains having a grain size of 20-60 nm were dispersedin an amorphous matrix. With X-ray analysis, a clear diffraction peakwas not confirmed.

[0067] Additionally, the substrate having the film formed thereon washeat treated in a vacuum for one hour at 180° C.

[0068] Through X-ray analysis of the film after the heat treatment,clear diffraction peaks were confirmed, and it was further determinedthat crystal grains having an average grain size of 240 nm werecontained in the film. An SEM picture of the surface of the film of thepresent example is shown in FIG. 2. Through SEM observation, it wasconfirmed that the film was an aggregate of crystal grains, i.e., apolycrystalline film, and that the film had a flat surface, the heightvariation of irregularities being 20 nm or less. In the surface of thefilm, although crystal grain boundaries could be confirmed, boundariesbetween regions in which crystal grains orient in approximately the samedirection, ire., domains, could not be discerned.

[0069] The resistivity of the film of the present example was 3.6×10⁴Ω·cm, and the transmissivity with respect to light having a wavelengthof 400 nm was 83%. The film demonstrated excellent alkali resistance.After the formation of the film, almost no bend in the substrate 5 acould be discerned, and good adhesion between the film and the substrate5 a was confirmed. By etching the film formed on the substrate 5 a, apattern for the electrodes 7 a was processed, whereby the film wasprocessed into a fine pattern with high precision.

[0070] Films having the same composition as the film of example 1, buthaving not been subject to crystallization by heating were used ascomparative examples, and the characteristics of the films of eachexample were evaluated in the same manner. The results are shown inTable 1. TABLE 1 Comparative Comparative Example 1 Example 1 Example 2Film forming thickness (nm) 150 130 140 substrate — 100 150 temperature(° C.) gases introduced Ar, O₂ Ar, O₂ Ar, O₂ pressure (Torr*) 3.0 × 10⁻³3.0 × 10⁻³ 2.0 × 10⁻³ speed (nm/min)  6 6.5 7.5 Crystallizationtreatment temperature (° C.) 180 — — time (Hr)  1 — — atmosphere vacuum— — Film characteristics resistivity (Ω · cm) 3.6 × 10⁴ 5.0 × 10⁴ 2.2 ×10⁴ transmissivity (%)  83 60 80 at 400 nm crystal size (nm) 240 none 30domains none none observed alkali resistance good poor good reliabilitygood poor fair Substrate characteristics bend small small large adhesiongood good poor patternability good good poor

[0071] It was determined by X-ray analysis that the film of theComparative Example 1 formed at a substrate temperature of 100° C. is anamorphous material from which a diffraction pattern cannot besubstantially discerned. Thus, it is poor in terms of transmissivity andalkali resistance. The film of Comparative Example 2 formed at asubstrate temperature of 150° C. is, as shown in FIG. 8, apolycrystalline film having a grain size of 30 nm, and while excellentin terms of resistivity, transmissivity, alkali resistance, and thelike, the bend in the substrate is large and additionally, adhesionbetween the substrate and the film and patternability are poor.

[0072] In other words, the present example makes it possible to form, ata low temperature, a conductive Elm that is excellent in terms of avariety of properties such as resistivity, transmissivity, chemicalresistance, corrosion resistance, patternability, and adhesion and tolessen the bend that arises in a substrate by the forming of such a filmon the substrate

EXAMPLE 2

[0073] In the present example, the present invention is described usinga substrate for a color liquid crystal display panel as the example.

[0074] The construction of a color liquid crystal display panel thatutilizes substrates with electrodes of the present example isschematically shown in FIG. 3. As shown in the figure, an undercoatlayer 6 a is formed on either side of a substrate 5 a, and an undercoatlayer 6 b is formed on either side of a substrate 5 b, the undercoatlayers 6 a and 6 b being made of, for example, silicon oxide. On asurface of the substrate 5 a that is opposed to the substrate 5 b,electrodes 7 a made of a transparent conductive material are formed witha buffer layer 10 disposed therebetween.

[0075] At the same time, a color filter layer 11 made of an organicmaterial is formed on a surface of the substrate 5 b that is opposed tothe substrate 5 a. Over the color filter layer 11, electrodes 7 b isformed with a resin layer 12, for forming a flat surface, disposedtherebetween.

[0076] An array substrate 2 a was fabricated utilizing a substrate 5 amade of an epoxy resin having a glass transition temperature of 170° C.and having a thickness of 0.2 mm.

[0077] After immersing the substrate 5 a in a polysilazane raw materialsolution (available from Tonen Chemical Corporation), the substrate 5 awas heat treated for 1 hour at 120° C. and for 3 hours at 95° C. and 80%RH, whereby, on either surface of the substrate 5 a, an undercoat layer6 a having a thickness of 30 nm and being made of silicon oxide wasformed. On one of the surfaces of the substrate 5 a, a cycloolefin resinraw material solution was then applied by spin coating, and thesubstrate was heated for 3 hours at 160° C. to form a buffer layer 10having a thickness of 1 μm. On the surface of the substrate 5 a havingthe buffer layer 10 formed thereon, an ITO film containing 3% by weightof tin oxide was formed by sputtering under the conditions shown inTable 2. Specifically, under an atmosphere in which argon has beenintroduced as the atmospheric gas to a pressure of 5.0×10⁻³ Torr (≈0.67Pa), an ITO film having a thickness of 210 nm was formed at a rate of 7nm/min. by performing sputtering on the surface of the substrate 5 awhile heating the substrate at 80° C.

[0078] Meanwhile, on either surface of a substrate 5 b similar to thesubstrate 5 a, an undercoat layer 6 b made of silicon oxide was formedin the same manner as was done with the substrate 5 a, and subsequently,on one of the surfaces of the substrate 5 b, a color filter layer 11 wasformed by printing and carrying out heat treatment for 5 hours at 160°C. The substrate 5 b was then immersed in acrylic resin raw materialsolution and heat treated for 3 hours at 160° C. to form a resin layer12 for planarization. On a surface on the side of the substrate 5 bhaving the color filter layer 11 formed thereon, an ITO film having athickness of 210 nm was formed in the same manner as was done with thesubstrate 5 a.

[0079] The ITO film formed over the substrate 5 a and that formed overthe substrate 5 b had a structure such that microcrystalline grainshaving a grain size of approximately 30-120 nm were dispersed in anamorphous matrix, and an X-ray diffraction peak was not discerned.Subsequently, by carrying out heat treatment for 3 hours at 160° C. inthe air, the ITO film was transformed into a polycrystalline film havingan average crystal grain size of 200 nm or larger, having surfaceirregularities with a height variation of 20 nm or less, and having nodomain boundaries.

[0080] The characteristics of the film and the substrate obtained wereevaluated in the same manner as with Example 1. The results are shown inTable 2. TABLE 2 Example 2 Film forming thickness (nm) 210 substrate 80temperature (° C.) gases introduced Ar pressure (Torr*) 5.0 × 10⁻³ speed(nm/min) 7 Crystallization treatment temperature (° C.) 160 time (Hr) 3atmosphere air Film characteristics resistivity (Ω · cm) 3.5 × 10⁴transmissivity (%) 80 at 400 nm crystal size (nm) 200 domains nonealkali resistance good reliability good Substrate characteristics bendsmall adhesion good patternability good

EXAMPLE 3

[0081] In the present example, the present invention is described usinga substrate for a color liquid crystal display panel having anotherconstruction as an example.

[0082] The construction of a color liquid crystal display panel thatutilizes substrates with electrodes of the present example isschematically shown in FIG. 4. An array substrate 2 a is the same asthat used in Example 2. On the other hand, a counter substrate 2 b has aresin layer 12 for planarization formed only on the surface opposing thearray substrate 2 a. On the top surface, a buffer layer 10 like thatprovided over the array substrate 2 a is formed.

[0083] Substrates 5 a and 5 b made of a silicon ladder-type curedsilicone resin having a thickness of 0.35 mm and having a glasstransition temperature of 200° C. were utilized to fabricate an arraysubstrate 2 a and a counter substrate 2 b, respectively.

[0084] The array substrate 2 a was fabricated in the following manner.On either side of the substrate 5 a, an undercoat layer 6 a having athickness of 15 nm and being made of silicon oxide was formed bysputtering. On one of the surfaces of the substrate 5 a, a buffer layer10 having a thickness of 1 μm and being made of a cycloolefin resin wasthen formed in the same manner as Example 2. On the surface of thesubstrate 5 a having the buffer layer 10 formed thereon, an ITO filmcontaining 7% by weight of tin oxide was formed by sputtering under theconditions shown in Table 2. Specifically, under an atmosphere in whichargon and oxygen has been introduced as atmospheric gases to a pressureof 5.0×10⁻³ Torr (≈0.67 Pa), an ITO film having a thickness of 120 nmwas formed at a rate of 6 nm/minute by performing sputtering on thesurface of the substrate 5 a while heating the substrate at 120° C.

[0085] Meanwhile, the counter substrate 2 b was fabricated as describedbelow. In the same manner as with the substrate 5 a, an undercoat layer6 b made of silicon oxide was formed on either side of the substrate 5b, and subsequently, on one of the surfaces of the substrate 5 b, acolor filter layer 11 was formed by printing and carrying out heattreatment for 5 hours at 170° C. On the color filter layer 11, acycloolefin resin raw material solution was applied by spin coating, andthe substrate was heated for 3 hours at 170° C. to form a buffer layer10 having a thickness of 1 μm. On the surface of the substrate 5 bhaving the buffer layer 10 formed thereon, an insulating layer 13 havinga thickness of 15 nm was formed by sputtering and on this, an ITO filmcontaining 7% by weight of tin oxide was formed in the same manner aswith substrate 5 a.

[0086] The ITO film formed over the substrate 5 a and that formed overthe substrate 5 b had a structure such that microcrystalline grainshaving a grain size of approximately 60-180 nm were dispersed in anamorphous matrix, and a clear X-ray diffraction peak was not discerned.Subsequently, by carrying out heat treatment for 1 hour at 170° C. in avacuum, the ITO film was transformed into a polycrystalline film havingan average crystal grain size of 100 nm, having surface irregularitieswith a height variation of 20 nm or less, and having no domainboundaries.

[0087] The characteristics of the film and the substrate obtained wereevaluated in the same manner as with Example 1. The results are shown inTable 3. TABLE 3 Example 3 Film forming thickness (nm) 120 substrate 120temperature (° C.) gases introduced Ar, O₂ pressure (Torr*) 5.0 × 10⁻³speed (nm/min) 7 Crystallization treatment temperature (° C.) 160 time(Hr) 3 atmosphere vacuum Film characteristics resistivity 3.4 × 10⁴ (Ω ·cm) transmissivity 82 (%) at 400 nm crystal size (nm) 100 domains nonealkali resistance good reliability good Substrate characteristics bendsmall adhesion good pattern ability good

EXAMPLE 4

[0088] Using glass substrates having a thickness of 0.4 mm forsubstrates 5 a and 5 b, an array substrate 2 a and a counter substrate 2b were fabricated in the same manner as Example 1. The thickness ofundercoat layers 6 a and 6 b was made to be 200 nm and the thickness ofITO films 200 nm.

[0089] The characteristics of the film and the substrate obtained areshown in Table 4. In addition, for Comparative Examples 3 and 4, a sameglass substrate was used and a film was formed on each in the samemanner as with Comparative Examples 1 and 2. The characteristics ofthese films and substrates are shown in Table 4.

EXAMPLE 5

[0090] Using glass substrates having a thickness of 0.55 mm forsubstrates 5 a and 5 b, an array substrate 2 a and a counter substrate 2b were fabricated in the same manner as Example 2. The thickness of theformed ITO films was made to be 140 nm.

[0091] The characteristics of the film and the substrate obtained areshown in Table 4.

EXAMPLE 6

[0092] Using glass substrates having a thickness of 0.55 mm forsubstrates 5 a and 5 b, an array substrate 2 a and a counter substrate 2b were fabricated in the same manner as Example 3. The thickness of ITOfilms formed was made to be 90 nm.

[0093] The characteristics of the film and the substrate obtained areshown in Table 4. TABLE 4 Comparative Comparative Example 4 Example 5Example 6 Example 3 Example 4 Film forming thickness (nm) 200 140  90130 140 substrate —  80 120 100 150 temperature (° C.) gases introducedAr, O₂ Ar Ar, O₂ Ar, O₂ Ar, O₂ pressure (Torr*) 3.0 × 5.0 × 5.0 × 3.0 ×2.0 × 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³ speed (nm/mm)  6  7  7 6.5 7.5Crystallization treatment temperature (° C.) 180 160 160 — — time (Hr) 1  3  3 — — atmosphere vacuum air vacuum — — Film characteristicsresistivity (Ω · cm) 3.6 × 10⁴ 3.5 × 10⁴ 3.4 × 10⁴ 5.0 × 10⁴ 2.2 × 10⁴transmissivity (%)  83  80  82  60  80 at 400 nm crystal size (nm)240 >200 100 none  30 domains none none none none observed alkaliresistance good good good poor good reliability good good good poor fairSubstrate characteristics bend small small small small large adhesiongood good good good poor patternability good good good good poor

[0094] As described in the examples above, the present invention makesit possible to form a conductive film that reduces the bend in asubstrate and that shows good characteristics at a low temperature, byperforming sputtering at a low temperature to form on a substrate aconductive film that is either amorphous or is such that crystal grainsare contained only to the extent that a clear X-ray diffraction peakcannot be observed and by heat treating this film so that it istransformed into a polycrystalline film.

EXAMPLE 7

[0095] In the present example, a substrate with electrodes is describedin which bend in the substrate is suppressed with even greater results.

[0096] A schematic view of the substrate with electrodes of the presentexample is shown in FIG. 5. Transparent electrodes 102 a formed on asurface of a substrate 105 made of a synthetic resin are covered with aconductive coating film 100 having a pattern that substantially matchesup with the transparent electrodes.

[0097] In the manner described as follows, a substrate 101 a withelectrodes and a substrate 101 b with an electrode shown in FIG. 5 wereformed. On a surface of a substrate 105 being made of acrylic resin,having a thickness of 0.2 mm, and having a square shape with a sidelength of 30 cm, a transparent metal film 102 having a thickness of 10nm and being made of a silver alloy containing 1% by weight of each ofpalladium and copper was formed by sputtering without heating, as shownin FIG. 6a. The resulting metal film 102 had a transmissivity (at awavelength of 400 nm) of 90% and a sheet resistance of approximately 3Ω/□. This resistance is lower than that of an ITO polycrystalline filmformed at a substrate temperature of 250° C. Though the transmissivityis slightly low, it is sufficient for usage. An acrylic-based positiveresist having dispersed therein 50% by weight of ITO fine particles witha diameter of several nm was applied to the formed metal film 102,exposed, and heated at 170° C. to form a conductive coating film 100, asshown in FIG. 6b, made of a resist having a thickness of 1 μm and havinga shape that substantially matches with the pattern of transparentelectrodes 102 a to be formed. Because of the presence of dispersed ITOfine particles, this conductive coating film 100 showed a low volumeresistance of 10¹⁰ Ω·cm. The transmissivity was 95%. The conductivecoating film 100 having been formed into a pattern was used as a maskand the metal film 102 was patterned using an etching liquid containingacetic acid, phosphoric acid, nitric acid, and water, thereby formingstripe transparent electrodes 102 a. Because the conductive coating film100 was mainly composed of a synthetic resin in order that itscoefficient of linear thermal expansion be substantially equal to thatof the substrate 105 made of a synthetic resin and because the metalfilm was thin in order to ensure transparency, bend in the substrate 105was suppressed even with heating. Bend was not observed in the resultingsubstrate 101 at room temperature (25° C.).

[0098] When an ITO film having a thickness of 100 nm was formed on asame resin substrate at a substrate temperature of 140° C., the ITO filmshowed a low sheet resistance of 30 Ω/□, but a bend of approximately 5mm was observed in the substrate having such a film formed thereon atroom temperature. It is necessary that such a large bend be correctedbefore steps of pattering the ITO film or assembling the display panel.In addition, in transporting the substrate during commercial production,handling is extremely difficult because a special fixture for correctingto the bend is necessary and the like.

[0099] By contrast, because, in the present invention, bend is smallunder room temperature and even during heating, the production processis greatly simplified. Note that it is preferable that the forming ofthe metal film not only be carried out at 100° C. or less but be in theneighborhood of normal temperature. In addition, when the film thicknessis thin, it is possible to have a small bend even at a slightly hightemperature.

[0100] Using the resulting substrate with electrodes, a simple matrixliquid crystal display panel as shown in FIG. 7 was assembled. On asurface of a substrate 105 a, transparent electrodes 102 a and aconductive coating film 100 were formed in the manner described above.Similarly, a translucent electrode 102 b having a thickness of 40 nm anda conductive coating film 100 were formed on a surface of a substrate105 b. The transmissivity of the transparent electrode 102 b was 30% andthe reflectivity 55%. On a surface of each of a pair of substrates 101 aand 101 b, alignment films 108 a and 108 b made of polyimide and havinga thickness of 50 nm were applied and fabrication completed by rubbing,and a liquid crystal material was then injected between the substratesseparated from one another by a distance of 4 μm to form a liquidcrystal layer 103. On either side of this stacked structure, a polarizer109 was attached, whereby a transflective liquid crystal panel wasobtained. When the obtained liquid crystal panel was driven, variationsin cell thickness could be suppressed because change in the shape of thesubstrate was minimal, and thus, better image quality could be displayedin a wide temperature range and in a wide viewing angle range of from−40 degrees to 70 degrees with respect to the liquid crystal panelscreen than can be displayed by a liquid crystal panel utilizing aconventional ITO film for the electrodes and synthetic resin substratesfor the substrates.

[0101] Because the volume resistance of the conductive coating film 100is 10¹⁰ Ω·cm and the film thickness 1 μm, the film has a smallerimpedance than that of the liquid crystal layer 103. Even if the filmthickness is large, there is almost no image quality degradation causedby voltage division. As long as the volume resistance of the coatingfilm 100 is approximately less than 10¹² Ω·cm, image degradation isminimal. It is preferable that the resistance be low. At the present,however, it is difficult to obtain a resin coating film having aresistance of 10² Ω·cm or less. An organic conductive material havingsuch a low resistance, if available, may be used for the electrodeswithout using the coating film 100. Alternatively, using a resist resinfor the resin coating film that covers the thin film metal electrodes,as is the case in the present example, makes it possible to, not onlysuppress bend, but to simplify the steps. Even if the resin coating filmis not a resist, so long as it is provided with conductivity andtransparency, the advantageous effect of suppression in bend in thesubstrate necessarily results because the coefficient of thermalexpansion is similar to that of the resin substrate. In addition,pigment may be dispersed throughout the resin coating film such thatspecified colors of light only are transmitted.

[0102] It is even more effective to form such a film on a substrate ofan organic EL device. In the case of a substrate for an organic ELdevice, generally, as is shown in FIG. 7, a transparent electrode 202made of ITO or the like is formed on a substrate 205, and subsequently,a light-emitting layer 204, an electron transporting layer 205 made ofan organic substance, and a hole injecting layer 206 made of an organicsubstance are formed to serve as a light-emitting region 200. Areflective electrode 207 made of aluminum or the like is then formed. Aconductive coating film 208 may be formed, for example, as a resist foruse during the forming of the reflective electrode. As for use of aresin substrate, no problems arise in the formation of thelight-emitting region 200, which can be formed at a low temperature, butin the formation of the transparent electrode 202 that is made of ITO orthe like and heated at a relatively high temperature, the substrate issubject to bend, also creating a non-symmetric structure. If anything,bend in the substrate that varies according to temperature is a moreserious problem than in a liquid crystal display panel. The presentinvention makes it possible to realize an EL display device using resinsubstrates that has a small bend in the substrates in a wide temperaturerange and has excellent reliability. Note that in an EL device with alarge driving current, there is a need for a resin coating film having alow resistance as compared with a liquid crystal display device,specifically, a resistance of at least 10¹⁰ Ω·cm or less. When a metalthin film is used for the transparent electrode, film thickness is made20 nm or less, and preferably 10 nm or less.

INDUSTRIAL APPLICABILITY

[0103] With the present invention, a transparent conductive film thathas various excellent properties can be formed at a low temperature.Furthermore, bend in a substrate on which such a film is formed can besuppressed during formation of the film. Therefore, provision oflightweight display devices having excellent reliability is realized.

What is claimed is:
 1. A substrate with an electrode comprising asubstrate and an electrode made of an oxide conductive film disposed onthe substrate, wherein the electrode is composed of polycrystal havingan average grain size of 25 nm or larger, a crystal being the largestconstitutional unit having a boundary identifiable by surfaceobservation.
 2. The substrate with an electrode according to claim 1,wherein the average grain size of the crystals is 40 nm or larger. 3.The substrate with an electrode according to claim 1, wherein theaverage grain size of the crystals is 300 nm or less.
 4. The substratewith an electrode according to claim 1, wherein the thickness of theelectrode is in the range of 50 nm to 500 nm.
 5. The substrate with anelectrode according to claim 1, wherein height variation of a surface ofthe electrode is 20 nm or less.
 6. The substrate with an electrodeaccording to claim 1, wherein the oxide conductive film is made ofindium oxide doped with tin.
 7. The substrate with an electrodeaccording to claim 6, wherein the oxide conductive film has a tin oxidecontent of less than 5% by weight.
 8. The substrate with an electrodeaccording to claim 1, further comprising an undercoat film between thesubstrate and the oxide conductive film, the undercoat film being madeof an organic material.
 9. The substrate with an electrode according toclaim 1, wherein the substrate is made of a synthetic resin.
 10. Thesubstrate with an electrode according to claim 9, further comprising atransparent coating film on a surface of the electrode, the transparentcoating film containing a synthetic resin and having a volume resistancein the range of 10² Ω·cm to 10¹² Ω·cm.
 11. The substrate with anelectrode according to claim 10, wherein the transparent coating filmhas a thickness in the range of 0.5 μm to 5 μm.
 12. The substrate withan electrode according to claim 10, wherein the thickness of theelectrode is 20 nm or less.
 13. A method of producing a substrate withan electrode, comprising the steps of: forming an oxide conductive filmconsisting of an amorphous material or substantially consisting of anamorphous material on a substrate at a temperature equal to or less thanthe crystallization temperature of the film; and crystallizing the oxideconductive film by heating.
 14. The method of producing a substrate withan electrode according to claim 13, wherein in the step of forming anoxide conductive film, the oxide conductive film is heated at atemperature of 150° C. or less.
 15. The method of producing a substratewith an electrode according to claim 13, wherein in the step ofcrystallizing the oxide conductive film, the oxide conductive film isheated at a temperature equal to or less than the crystallizationtemperature.
 16. The method of producing a substrate with an electrodeaccording to claim 13, wherein in the step of crystallizing the oxideconductive film, the oxide conductive film is heated at temperatureequal to or less than the glass transition temperature of the substrate.17. The method of producing a substrate with an electrode according toclaim 13, wherein the step of crystallizing the oxide conductive film iscarried out in an atmosphere free of oxygen.
 18. The method of producinga substrate with an electrode according to claim 13, wherein the oxideconductive film is made of indium oxide having a portion substituted bytin.
 19. The method of producing a substrate with an electrode accordingto claim 18, wherein the oxide conductive film has a tin oxide contentof less than 5% by weight.
 20. The method of producing a substrate withan electrode according to claim 13, wherein, in the oxide conductivefilm to be formed on the substrate, crystal grains having an averagegrain size of 200 nm or less are dispersed in an amorphous matrix. 21.The method of producing a substrate with an electrode according to claim13, wherein, in the step of crystallizing the oxide conductive film, theoxide conductive film is transformed into an aggregate ofrandomly-oriented crystals having an average grain size of 20 nm orlarger.
 22. The method of producing a substrate with an electrodeaccording to claim 21, wherein the average grain size of the crystals is300 nm or less.
 23. The method of producing a substrate with anelectrode according to claim 13, wherein the thickness of the oxideconductive film is 500 nm or less.
 24. The method of producing asubstrate with an electrode according to claim 13, wherein the substrateis made of a synthetic resin.
 25. The method of producing a substratewith an electrode according to claim 13, wherein the substrate comprisesa undercoat film on a surface where the oxide conductive film is to beformed, the undercoat film being made of an organic material.
 26. Themethod of producing a substrate with an electrode according to claim 13,wherein, in the film completed by crystallization, the average grainsize of crystal grains is in the range of 20 nm to 300 nm.
 27. Themethod of producing a substrate with an electrode according to claim 13,further comprising a step of forming a transparent coating film on asurface of the electrode, the transparent coating film containing asynthetic resin and having a volume resistance in the range of 10² Ω·cmto 10¹² Ω·cm.
 28. The method of producing a substrate with an electrodeaccording to claim 27, wherein after forming a layer made of alight-curing resin on the completed oxide conductive film and exposingregions of the layer corresponding to an electrode pattern forprocessing the oxide conductive film to cure and form the transparentcoating film, the oxide conductive film is processed into the electrodeby etching the oxide conductive film with the cured transparent coatingfilm serving a resist.
 29. The method of producing a substrate with anelectrode according to claim 27, wherein the thickness of thetransparent coating film is in the range of 0.5 μm to 5 μm.
 30. Themethod of producing a substrate with an electrode according to claim 27,wherein the thickness of the electrode is 20 nm or less.